JPS5910487B2 - force transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a force transducer that applies force to a vibrator and obtains a signal corresponding to the force from the natural frequency of the vibrator.

Conventional force transducers of this type have poor temperature characteristics.

The reason for this is that the Young's modulus of the vibrator (spring metal) changes due to temperature changes, and the natural frequency changes.

Another problem is that drift occurs due to changes in Young's modulus over time.

An object of the present invention is to solve the above problems, that is, to provide a vibrating density meter that has excellent temperature characteristics and does not cause drift.

The present invention will be described in detail below using the drawings.

The figure is a configuration diagram showing an embodiment of a force transducer according to the present invention.

In the figure, reference numeral 1 denotes a plate-shaped vibrator with one end fixed and a force to be converted (measured) applied to the other end.

The part that actually operates as a vibrator is the central thin part 101
It is.

2 and 3 are piezoelectric elements for vibration detection, and 4 and 5 are piezoelectric elements for driving.

The piezoelectric element 2.3 and the piezoelectric elements 4, 5 have opposite polarities.

The piezoelectric elements 2 and 4 are attached to face each other at one end of the thin part 101, and the piezoelectric elements 3 and 5 are attached to face each other to the other end of the thin part 101.

6 and 7 are charge amplifiers that receive the output signals of the piezoelectric elements 2 and 3, respectively; 8 and 9 are coefficient circuits that subtract a certain value from the output signals of the charge amplifier 7; and 10 are coefficient circuits that add the output signals of the charge amplifier 6 and the coefficient circuit 8. An adder circuit 11 subtracts the output signal of the coefficient circuit 9 from the output signal of the charge amplifier 6 (it is a subtraction circuit).

Further, 12 and 13 are low-pass filters that pass frequencies of vibration modes of the second order or lower, and 14 and 15 are amplifiers that receive the output signals of the low-pass filters 12 and 130, respectively, and output voltages with constant amplitudes.

16 is an addition circuit that applies the sum of the output signals of the amplifiers 14 and 15 to the piezoelectric element 4; 17 is a subtraction circuit that applies the result obtained by subtracting the output signal of the amplifier 15 from the output signal of the amplifier 14 to the piezoelectric element 5. , 18 are output circuits that receive the output signals Ve, Vf of the amplifiers 14, 15) and output a signal corresponding to the power to be converted F.

The piezoelectric elements 2 to 5, the charge amplifier 6.7, the coefficient circuits 8 and 9, the addition circuits 10 and 16, the subtraction circuit IL17, the low-pass filter 12.13, and the amplifiers 14 and 15 are as follows:
It constitutes a driving section for driving the vibrator 1.

There is a difference between the signal output from one point on the closed loop made up of the drive unit and the vibrator 1 and the signal returned after completing one cycle with respect to the signal components of the primary and secondary vibration modes (more precisely, , for the signal passing through the filter 12 side, the first-order vibration mode, and for the signal passing through the filter 13 side, the second-order vibration mode). It is configured.

Therefore, in the steady state of operation, the charge amplifier 6.7 outputs the following signals Va and Vb.

The specific configuration of the coefficient circuits 8 and 9 is as follows:
m2/m2', m17 m for the output signal of
1' (m2 and m2' are signals in the same mode, and ml and ml' are signals in the same mode, so the ratio of these can be said to be constant).
If m1 = m1' and m2 = m2', the coefficient circuit 8°9 is unnecessary).

Therefore, the output signal V of the addition circuit 10 and the subtraction circuit 11
c, Vd are as follows.

As is clear from equation (2), Vc and Vd are signals corresponding only to the primary and secondary vibration modes, respectively.

And the signal Ve corresponding to Vc, Vd,
Vf is output from the amplifiers 14 and 15, and the addition circuit 16 and subtraction circuit 17 that receive this apply voltages to the piezoelectric elements 4 and 15 that reliably cause the vibrator 1 to vibrate in the primary and secondary vibration modes. 5.

The drive unit in this embodiment detects the vibration of the vibrator 1 only for signals caused by the primary and secondary vibration modes. Since the structure is such that a deforming force is applied to the vibrator 1, the vibrator 1 vibrates in a double vibration mode (primary and secondary) in an extremely stable state.

If the natural frequencies of the vibrator 1 at this time are fl (frequency for the first vibration mode) and f2 (frequency for the second vibration mode), then the following formula % formula % In other words, the sensitivity is Although there is a slight disadvantage of a decrease of 25%, there is a great advantage of being able to drastically reduce the influence of Young's modulus to 0.2%.

The output circuit 18 includes amplifiers 14 and 1 corresponding to fl and f2.
50 receives the output signals Ve and Vf, calculates the external force F using equation (4), and outputs a signal corresponding to this.

In the above explanation, the case where the vibrator 1 is vibrated simultaneously in dual vibration modes (primary and secondary) is shown, but it is also possible to vibrate the vibrator 1 in a time-sharing manner, for example, alternately in the primary and secondary vibration modes. It can also be configured to vibrate.

Further, although an example using a plate-shaped vibrator 1 has been shown, the same effect can be obtained using a vibrator having another shape (for example, a cylindrical shape).

Furthermore, although an example has been shown in which vibration detection and driving of the vibrator 1 are performed using a piezoelectric element, it is of course possible to configure the vibrator 1 using other means.

Further, although an example has been shown in which the vibration is performed in the primary and secondary vibration modes, the same effect can be applied to other vibration modes.

Furthermore, although an example using a plurality of piezoelectric elements for vibration detection has been shown, if the filters 12 and 13 alone can separate the signal into primary and secondary signals, one is sufficient.

In addition, an example was shown in which mode rejection on the drive side was performed using a plurality of drive piezoelectric elements, but in practice, even one piezoelectric element is sufficient for operation.

As explained above, according to the present invention, it is possible to realize a vibrating force transducer that is not affected by Young's modulus, that is, a force transducer that has excellent temperature characteristics and does not cause drift.

[Brief explanation of the drawing]

The figure is a configuration diagram showing one embodiment of a force transducer according to the present invention. 1... Vibrator, 2, 3... Piezoelectric element for vibration detection, 4.5... Piezoelectric element for drive, 6, 7
...Charge amplifier, 8,9...Coefficient circuit, 10,16...Addition circuit, 11,17...
...Subtraction circuit, 12, 13... Filter, 14, 15... Amplifier, 18... Output circuit.

Claims (1)

[Claims] 1. In a force transducer that applies force to a vibrator and obtains a signal corresponding to the force from the natural frequency of the vibrator, the vibrator is vibrated in multiple vibration modes simultaneously or in a time-sharing manner. A force transducer configured to calculate force from the natural frequency of each vibration mode when 2 Attach a plurality of piezoelectric elements for vibration detection to the vibrator and add or subtract the output signals of these piezoelectric elements to separate and extract signals corresponding to the natural frequencies of at least two types of vibration modes, and use this signal to The force transducer according to claim 1, wherein the force transducer is configured to operate a drive piezoelectric element attached to the vibrator.